Without limiting the scope of the present invention, its background will be described in relation to a safety system of a subsea well installation, as an example.
In certain subsea well installations, the safety systems may include a subsea safety tree on the lower end of a tubular string that may be positioned within the blowout preventer stack of a subsea wellhead. The subsea safety tree may include one or more shut-in valves that operate to automatically shut-in the well in the event of emergency conditions. In addition, the subsea safety tree may include a latch assembly that enables separation of the tubular string from the lower portion of the subsea safety tree, a retainer valve that prevents fluid discharge from the tubular string into the environment and a vent sleeve that provides for controlled venting of pressure trapped between the closed retainer valve and the closed shut-in valves of the subsea safety tree.
Conventionally, each of these components of the subsea safety tree, the retainer valve, the vent sleeve, the latch assembly and the shut-in valves, are controlled by fluid pressure in control lines which extend from a pressure source at the surface to the subsea safety tree. In many installations, dedicated control lines between each of the components and the surface are used, including both supply lines and return lines. In addition, the actuation of each of these components is controlled by electrical switches, such as solenoid valves, that selectively prevent and allow hydraulic pressure to operate the various components. In an emergency situation, the proper operation of these components is necessary to safely shut-in the well, contain fluid within the tubular string, bleed off pressure between the shut-in valves and the retainer valve and cause separation of the tubular string from the subsea well installation.
It has been found, however, that certain operations such as gravel packing, fracturing or fracture packing, that require proppant laden slurry to be pumped into the well through the tubular string, may result in damage to or debris buildup within components of the subsea safety tree. This damage or debris buildup may prevent proper operation of one or more of the components of the subsea safety tree. Accordingly, a need has arisen for systems and methods of protecting the components of the subsea safety tree during operations wherein proppant laden slurry is pumped into the well through a tubular string including a subsea safety tree.